Sports drinks: vital for hydration or a waste of money?

Do I really need a sports drink? Won't water do?

It depends on the intensity and duration of your workout. "Water is generally sufficient for shorter sessions, but for exercise lasting more than 60 minutes, an isotonic sports drink is recommended," says Wendy Martinson, registered dietician and sports nutritionist.

But Nick Morgan, head of sport science at Lucozade, believes sports drinks can be useful for shorter workouts, too: "If you've had a good high-carbohydrate meal in the three-four hours before your workout, you probably don't need a sports drink", he says. "But if you haven't eaten for ages - if, for example, you've just got up or have hit the gym straight after work, a sports drink will provide a little extra energy, helping you get more out of yourself and reducing your 'perception of effort.'"

Just for the record, a study in the Journal of Applied Physiology found that consuming an isotonic sports drink increased treadmill running time to exhaustion by 27% in recreational runners.

What should I look for in a sports drink?

According to Martin Gibala, an associate professor of kinesiology at McMaster University in Canada, there are two key ingredients in a good sports drink: "Carbohydrate, which provides fuel for working muscles, and sodium, which helps to maintain fluid balance."

But formulation is key. An isotonic drink (such as Lucozade Sport or Gatorade) contains a 6-8% carbohydrate solution, which is absorbed into the body more rapidly than water, as well as providing energy. A sports drink should also contain approximately 50mg of sodium per 100ml, along with smaller amounts of the other electrolytes, such as potassium and chloride, which are lost in sweat.

Morgan highlights another important consideration: palatability. "Studies show clearly that if you don't like the taste of a sports drink, you won't consume enough of it."

At the other end of the scale are 'hypertonic' drinks, with a carbohydrate concentration greater than 10%. "These will have a slow gastric emptying rate, thus decreasing fluid absorption," says Martinson. Energy drinks - including Red Bull - and soft drinks - such as Coke and Pepsi - come into this category, which makes them unsuitable for use during exercise.

How much do I need to drink?

In 2007, the American College of Sports Medicine, an international authority on sport science, revised its guidelines on fluid intake during physical activity, no longer suggesting specific volumes per hour. "We now know that individual needs vary so much it is impossible to suggest a 'one size fits all' amount that will suit everyone", says Morgan. "Issues surrounding the risks of dehydration on one hand and hyponatraemia (water intoxication) on the other make this dangerous ground."

So what's the best way forward? Martinson advises calculating your own personal 'sweat rate' (see below) so that you can determine how much you need to drink. "Exercise performance is impaired when there is only a 2% decrease in body weight [due to fluid loss]", she says. "Determining your own sweat rate will enable you to drink sufficient amounts of fluid to minimise weight loss to less than 2% body weight."

According to Joseph Verbalis, Professor of the Department of Medicine at Georgetown University Medical Center, you should also listen to your body. "Thirst is a good indicator of your body's need for fluid," he says.

Working out your sweat rate

• Record your nude pre-training weight (in kg) • Record your nude post-training weight, towelling off sweat first.• Opt for a 30- or 60-minute session, during which you don't consume fluid. (This makes the maths easier!)• Subtract your post-training weight from pre-training weight to work out the weight lost, and multiply by 1,000 to convert to grams. The amount you lost in grams is equal to the amount of fluid you lost during that session. If you did a 30-minute session, multiply by two to get your ml per hour figure. This is the amount you should aim to consume in subsequent sessions. For example, if you lost 500g in 30 minutes, you'd be looking to consume 1000ml per hour.• Bear in mind that the temperature, weather conditions and the intensity of the session will influence your fluid loss - factor this in when determining how much to drink in future sessions.

Should I drink before my workout, or just during?

It's important to start exercise well hydrated. Research suggests that the body cannot absorb ingested carbohydrate efficiently if the body is dehydrated, so even if you are guzzling sports drinks, they may be of limited benefit. The ACSM recommends drinking 5-7ml of fluid per kg of your body weight in the three-four hours before exercise. (So, if you weigh 60kg that means drinking 300-420ml.) If your urine is still dark after this, they suggest drinking a further 3-5ml/kg. Water will do just fine - but, says Martinson, consuming a sports drink helps to top up carbohydrate stores.

Does it matter if I drink sports drink and water in the same session?

Martinson believes not. "You will still benefit from the carbohydrate and electrolytes in the sports drink even if you drink some water as well," she says.

Scientists at the Gatorade Sports Science Institute, however, disagree, stating: "Watering down a sports drink dilutes the taste, carbohydrate content and electrolyte level - any of which will diminish its performance benefits."

What about if I mix sports drinks with gels? Am I destined for the Portaloo?

Despite a belief among many runners and triathletes that you shouldn't mix drinks and gels, according to Morgan it shouldn't make any difference. "The important thing is to get enough fluid and enough carbohydrate on board - whatever the source," he says. But like any nutrition or hydration strategy, you need to test it out in training.

Once I've finished exercising, is there any benefit in drinking a sports drink?

"You need to think about what kind of workout you've done and when you'll next be exercising to determine whether a sports drink will help you recover," says Morgan. If you've swanned around the gym for 20 minutes, forget it. If, however, you've done a tough session and will probably be doing another one within the next 48 hours, you'll definitely benefit from taking extra carbohydrate on board within the first hour.

"Research also supports the practice of consuming protein after exercise to promote muscle recovery," adds Gibala. Proprietary 'recovery' sports drinks typically tick both the carb and protein boxes, but research from Northumbria University found chocolate milk to be highly effective in facilitating recovery.

Other recent research, published in the Journal of Applied Physiology, found that athletes who added caffeine to their recovery cocktail had 66% more glycogen in their muscles four hours after finishing an intense workout.

I have 'tidemarks' on my clothes after exercise - should I take extra salt on board?

Tidemarks on clothes are an indication of a 'salty sweater'. But, says Morgan, this alone is not reason to take extra salt on board. "It needs to be considered alongside the volume you sweat: so you could be a salty sweater who doesn't lose much sweat (so not too much sodium lost) or a non-salty sweater who sweats buckets (increased loss of sodium.) If you sweat profusely and are a salty sweater there may be need for extra salt, but you would probably be suffering from cramping or extreme fatigue if this were the case."